Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$93.79	6.321%	$99.7185	$99.72	$99.70	$99.70
Purchase #2	$25.82	5.790%	$27.315	$27.32	$27.30	$27.30
Purchase #3	$244.27	4.625%	$255.5675	$255.57	$255.55	$255.60
Purchase #4	$127.92	13.528%	$145.225	$145.23	$145.25	$145.20
Purchase #5	$44.37	6.372%	$47.1973	$47.20	$47.20	$47.20
Purchase #6	$117.39	13.198%	$132.8831	$132.88	$132.90	$132.90
Purchase #7	$101.54	7.251%	$108.9027	$108.90	$108.90	$108.90
7 purchase totals =	$755.10		$816.8091	$816.82	$816.80	$816.80